Aluminum-titanium master alloys



ALUMINUM-TITANIUM MASTER ALLOYS Stephen F. Urban, Kenmore, N.Y.,assignor to National Lead Company, New York, N.Y., a corporation of NewJersey No Drawing. Application November 21, 1956 Serial No. 623,735

1' Claim. (Cl. 75-438)- This invention relates to aluminum-titaniumalloys and is particularly concerned with such alloys in which thetitanium content is between about 6% and about 20%.

Titanium is extensively used in aluminum alloys as a grain refiningagent. For this purpose, it is added in amounts up to about 0.25% toalloys such as those of the Al-Zn, Al-Zn-Mg and Al-Cu types. A methodused widely by producers of aluminum alloys for introducing the desiredamount of titanium into the alloys has been the addition to the moltenalloy of so-called master alloys containing 2V2%6% titanium with theremainder aluminum. These master alloys have, prior to the presentinvention, been made by diluting a 50% Ti-50% Al alloy with moltenaluminum at temperatures of 2200 F. to 2400 F. Since this is arelatively expensive method of preparation and since, because of the lowtitanium content, they must be used in rather large amounts, such masteralloys have not been entirely satisfactory commercially. Use of Al-Tialloys of this type containing more than about 6% titanium has not beenfeasible because of the slow rates at which such alloys dissolve inmolten aluminum and aluminum alloys at the preferred workingtemperatures of l300 F.-l400 F. and the low recoveries of dissolvedtitanium in the final alloys.

.It is an object of the present invention to provide Al-Ti master alloyscontaining from about 6% to 20% titanium which are readily soluble inaluminum and aluminum alloys at the desired working temperatures.

Another object of the present invention is to provide Al-Ti masteralloys containing from 6% to 20% 'tanium which have novel and usefulstructures.

A further object of the present invention is to provide Al-Ti masteralloys containing 6% to 20% titanium which are useful for the additionof titanium to aluminum and aluminum base alloys.

Other objects and advantages of the present invention will be apparentfrom the following description thereof.

It has been discovered that, unlike the master alloys discussed above,Al-Ti master alloys containing about 6% to 20% titanium which areproduced by a process of an entirely diiferent type not hitherto usedfor this purpose readily dissolve in molten aluminum and aluminum alloysat the normal working temperatures of 1300" F.-l400 F. These solublemaster alloys, it has been found, have a structure that is quite unlikethe structure of Al-Ti alloys of similar composition formed by mixingthe molten metals.

The difference in structure mentioned above is readily seen bycomparison under the microscope of unetched specimens of the two typesof alloys. In so examining Al-Ti master alloys made by the process ofthe present invention it will be observed that the intermetalliccompound Al Ti appears as light particles which are relatively small andnodular or rounded in shape. In contrast, the Al Ti particles in anAl-Ti master alloy made by the previously used method of diluting a 50%Ti- 50% Al alloy with molten aluminum at temperatures between 2200' F.and 2400 F. are large and acicular or needle-like. This is found .to bethe case even though the titanium contents ofthe two alloys areapproximately identical. Moreover, it has been ascertained that the sameditierence in structure is found in alloys of the two types where thetitanium contents range from approximately 20% down to about 6%, the AlTi particles in alloys produced by the present process being presentessentially in nodular or rounded form.

The novel master alloys of the present invention are produced byreacting an alkali-metal fiuotitanate such as K TiF with aluminum. Whilethe precise reaction involved is not certain, it is believed that it mayproceed v with some of thealuminu'm according to the following equation:

The titanium thus liberated combines, of course, with aluminum to formthe intermetallic compound Al Ti.

The following examples illustrate the use of the abovedescribed methodin producing novel Ai-Ti master alloys according to the presentinvention.

Example I 46 parts of aluminum was melted in a graphite crucible and25.5 parts of potassium fluotitanate (K TiF was added thereto in smallincrements with stirring, the temperature of the bath being maintainedat about l500 F. or above. After all the K TiF was mixed in, the moltenspent salt on top of the bath was ladled oil and the metal was pouredinto cast-iron ingot molds. The ingots thus produced were analyzed andfound to contain 6.3% titanium.

Example 2 Aluminum parts) was melted in a graphite crucible and broughtto a temperature of 1600 F. To the molten metal there was added 50 partsof K TiF in increments with stirring after each addition. When theaddition was completed the supernatant spent salt was decanted from thecrucible and the metal was poured into cast iron ingot molds. Analysisof the ingots showed an 11.6% titanium content.

Example 3 Forty parts of aluminum was placed in a graphite crucible andheated to 1300 F. Then 51 parts of K TiF was added, a little at a time,to the molten aluminum while maintaining the temperature. The .K TiF wasstirred into the bath and when the addition was completed the crucibleand contents were allowed to cool. The pig or ingot of metal removedfrom the cooled crucible was analyzed and 19.1% Ti was found.

In tests of novel master alloys produced in accordance with the presentinvention it has been found that, when added to molten aluminum attemperatures of 1300 F.-- 1400 F., they dissolve readily and give highrecoveries of dissolved titanium. In a number of such tests thedissolved titanium content of the finished aluminum alloys averaged oftheoretical content based on the amount of master alloy added.Comparative tests employing master alloys containing from 6%20% Ti madeby dilution of 50% Al-50% Ti alloys showed recoveries of between 20% and10% (average 14%) of theoretical. Solution of the latter master alloyswas very slow in all cases and in a test with such a master alloycontaining 27% Ti the master alloy did not even melt.

It will be evident from the foregoing that by the present inventionthere are provided novel and improved Al-Ti master alloys which arequite useful as alloying addition agents. These novel master alloys arecharacterized by being readily soluble in molten aluminum and aluminumalloys at the normal working temperatures of 1300 F.-1400 F. withresulting high titanium recovery.

3 They also are characterized by the occurrence of the Al Ti of thealloy essentially in dispersed nodular particles instead of theessentially acicular form characteristic of known master alloys ofsimilar compositions.

Aluminum-titanium master alloys containing more than about 20% Ti can beproduced by the process described above. However, excessively hightemperatures are required since the melting points of such alloys arehigh. Their use is, therefore, not ordinarily practical.

Likewise, of course, other alkali metal fluotitanates may be used inmaking Al-T i master alloys according to the invention. Potassiumfiuotitanate is preferred merely because of its greater availability.

Where, in the specification and the appended claim, parts or percentagesare stated or referred to, it is to be understood that these are partsor percentages by weight.

I claim:

An Al-Ti master alloy containing 6% to about 20% titanium with thebalance substantially aluminum and characterized by being readilydissolved in aluminum at temperatures of 1300 F.l400 F. and by theappearance in said master alloy of the Al 'l'i constituent essentiallyin nodular particles.

References Cited in the file of this patent UNITED STATES PATENTS451,404 Langley Apr. 28, 1891 451,405 Langley Apr. 28, 1891. 451,406Langley Apr. 28, 1891 15 2,781,261 Kamlet Feb. 12, 1957

